The invention relates to a method for producing and assembling superheater tubes of steam generators.
Superheater tubes are primarily used in steam generators of power plants that are heated with fossil fuels. In conjunction with that, the superheater tubes are arranged as heating surfaces in a gas flue which is surrounded by tube walls and which is located upstream, as viewed in the direction of flow of the combustion exhaust gas, of the combustion chamber which is constructed with burners, whereby the cross section of the gas flue and the combustion chamber is constructed in rectangular fashion in most cases. The tubes of the superheater tubes, which are formed of welded straight tubes and bends and possibly additional weld-on parts, carry within them a working medium heated by means of the combustion of the fossil fuel and superheated in the superheater tubes and pass it on to further processes. In the case of the known welded superheater tubes, usually 9-12% chromium steels are used with subsequent heat treatment, and/or austenitic steels with non-precipitation-hardened nickel-based alloys in a solution-annealed state that do not as a rule require heat treatment.
The desire for steam generators with higher efficiencies and the resulting development of the “700° C. power plant” with regard to the steam working medium in order to increase efficiency, which, among other things, help to decrease the emission of CO2 into the atmosphere, leads to an increase of the steam parameters of the steam generator, among other things. Achieving or realizing higher steam parameters, i.e., higher pressures and temperatures of the steam working medium, places high requirements on the materials that are to be used in the steam generator. The materials that are being used at the present time are unable to meet these requirements. Further development of the materials and their processing is thus unavoidable. Precipitation-hardened nickel-based alloys lend themselves as suitable materials for the realization of higher steam parameters in superheater tubes. In every case, these types of alloys require heat treatment of the complete tube, both the weld and bend areas as well as the basic tube of the superheater tubes.
The task of the present invention is to suggest a method for producing and assembling superheater tubes of steam generators in which the production and assembly takes place in a more efficient and practical way. In particular, it is the task of the invention to develop a method for the manufacturing and assembly sequence, as well as, in particular, the heat treatment of superheater tubes and their connecting pipes made primarily from precipitation-hardened nickel-based alloys, whereby this method should also include concepts in which a time-consuming heat treatment can be dispensed with or can at least be kept to a minimum.